Storage area networks (SANs) are networks of computer data storage devices that are attached to servers in such a way that they appear to each and every server to be a locally attached storage device, instead of a remotely attached storage device. The topography of a SAN is such that data travels according to one or more extremely high bandwidth interface, such as Infiniband, Fiber Channel, Ethernet, or SAS, and protocols such as SCSI. SANs are typically managed by a remote storage manager program, such as SANtricity, provided by LSI Corporation of Milpitas, Calif.
Storage manager software such as SANtricity optionally offer a volume snapshot feature that provides a point-in-time image of a SAN storage volume. The snapshot is the logical equivalent of a complete physical copy, but is created much more quickly and requires less disk space. Snapshot volumes appear and function as standard storage volumes. They are host-addressable and can be read, written to, or copied.
Volume snapshot enables nonproduction, backup, or analysis servers to access an up-to-date copy of production data while the production data remains online and user-accessible. Volume snapshot is designed for users whose data availability cannot be disrupted for routine management functions. Volume snapshot supports round-the-clock processing as it stages data for operations such as backup, data mining/analysis, and work distribution. In other words, some operations that do not tolerate continuous data access, such as a backup operation, can be performed on snapshot data instead of live data. Thus, the process of taking a snapshot is not the same as merely making a backup.
This functionality requires minimal dedication of storage capacity, typically only about ten to twenty percent of the original SAN volume, enabling the storage of several snapshots within the space required for a single mirror. However, snapshot volumes have the same high-availability characteristics as standard storage volumes, such as RAID protection and redundant path failover.
However, multiple snapshots do take some amount of space, and there is always an incentive to reduce the amount of space used by snapshots. What is needed, therefore, is a system for managing snapshots of a SAN.